Synergistic reduction of NO/SO2 through co-firing municipal sewage sludge with coal gangue
Yasen Wu, Li Zhang, Muxin Liu, Zhiping Lei, Zhan‐Ku Li, Weidong Zhang, Shibiao Ren, Zhicai Wang, Hengfu Shui, Jingchong Yan
Abstract
This study investigated co-combustion of sewage sludge (SS) and coal gangue (CG) as a sustainable waste disposal strategy that concurrently mitigated nitrogen oxides (NO) and sulfur dioxide (SO 2 ) emissions. Through a series of combustion tests under varied blending ratios and temperatures, comprehensive analyses of flue gases and ashes were performed to elucidate the underlying mechanisms of in situ pollutant reduction. The results revealed that compositional discrepancies in sulfur and nitrogen between SS and CG significantly affected emission dynamics. Thermally labile sulfur and nitrogen compounds in SS (e.g., organic sulfur, amino-nitrogen) prompted rapid emissions, contrasting with the gradual release of thermally stable sulfates, inorganic nitrogen, and quaternary nitrogen from CG. A two-stage description of NO release during co-combustion was proposed, implicating that the initial volatile-NO and subsequent char-NO emissions conformed with 3D diffusion (spherical symmetry) and shrinking core model, respectively. Oxygen-deficient conditions as well as homogeneous (CO-mediated) and heterogeneous (char-mediated) reactions contributed to the in situ conversion of NO into N 2 thus reducing NO levels in flue gas. Sulfur release dynamics adhered to a 3D diffusion model, with calcium-bearing compounds in ashes enhanced SO 2 capture thus reducing its emission during co-combustion. The synergistic reduction of NO and SO 2 was notably affected by the co-firing ratios and temperatures. These findings confirm the dual benefits of SS-CG co-combustion, combining waste valorization with pollutant mitigation, making it a viable and efficient strategy for waste management and clean energy production.